[BillyPilgrim]

After owning several zooms I've settled on the Canon 300mm f/4 L IS with a 1.4x converter.

I found that I never got close enough to a bird or mammal to use a zoom on any setting other than maximum so it seemed a bit pointless having the zoom facility. Especially as there is a compromise on image quality with a zoom.

I dithered over the Canon 300mm f/4 and 400mm f/5.6 for some time but eventually chose the former for these reasons -

The excellent image quality is not noticably decreased when using the tele-converter. So you get 420mm at f/5.6 which is slightly better than the 400mm and you have the advantage of image stabilisation. Personally I find this invaluable as I do not carry a tripod or monopod.

Closest focus is just 1.5m. A full 2m shorter than the 400m which is great for close-ups of butterflies etc. It isn't true macro but if all you want is good close-up pictures then it does the job.